1. Field of the Invention
The present invention relates to a method and an apparatus for positioning a mobile terminal's location.
2. Description of Related Art
Wireless positioning services are referred to as Location-Based Services (LBS). A mobile communication network retrieves information on the location of a mobile communication gateway by a series of positioning techniques, and provides the information to a subscriber or others and the communication system, and thus implements a value-added service related to the location.
Generally speaking, all location-based services belong to LBS. Some services may have nothing to do with the location of the subscriber, such as weather at a fixed location or traffic routes between fixed start and end locations. However, in a mobile communication network, most LBS-relevant services have a close relationship with the location of the subscriber who holds the mobile terminal.
Before the implementation of mobile LBS, Global Positioning System (GPS) was applied in navigation and positioning services. With the development of mobile communication network technology, mobile LBS has been gradually applied and has matured since 1999. Presently, the mobile LBS realized via the mobile communication network is not only widely applied in special fields such as logistics management, traffic scheduling, medical rescue, field exploration and so on, but is also equally relevant for daily use.
At present, intense competition exists in the telecommunication industry. Mobile service operators are constantly striving to find new approaches to create new profit points or profit increase points. Mobile LBS is one of the services that bear the greatest potential market. In addition, with the continuous increase in the market of private cars, on-vehicle mobile communication platforms have great development potential. LBS for vehicle navigation and tracking represents a market with great development potential.
Practical applications of LBS include, but are not limited to, the following aspects:
1. Security application, e.g., emergency service and roadside help seeking, etc. If a subscriber becomes in danger at an unacquainted site, the subscriber can call the number of a rescue center (e.g., 110 in China, 911 in the U.S., 411 in Japan) as long as the user mobile phone supports LBS. The mobile communication network will automatically send information on the subscriber's location together with the user's voice information to the rescue center. Upon receiving the subscriber's call, the rescue center carries out rescue action rapidly and efficiently according to the obtained location information. In this way, the probability of successful rescue is drastically improved.
2. Information service application, e.g., daily life information and traffic information, etc. LBS can provide subscribers with map coordinates-related information services and interactive map information services. LBS can also provide subscribers with traffic conditions and optimal routes for car driving. LBS can help subscribers to locate nearby restaurants, cinemas, and other establishments around specified location. LBS can further provide value-added services like ticket booking and seat reservation. LBS can also be used in mobile yellow pages and mobile advertisements.
3. Tracking application, e.g., tracking vehicles or properties, etc. In a big city with high population density, traffic jams are serious issues, and growing requirements are put on vehicle navigation and intelligent transportation. As a core of an Intelligent Transportation System (ITS), an automatic vehicle positioning system provides functions such as dynamic traffic stream allocation, location navigation, emergent handling of accidents, safety precaution, vehicle tracking, vehicle scheduling and so on.
Early development of LBS dates back to the year of 1996. At that time, the Federal Communications Commission (FCC) publicized location requirements, which are referred to as E-911, and required that before Oct. 1, 2001, network operators should provide a positioning service with a precision of less than 1.25 feet to subscribers of mobile devices sending out E911 emergency calls. The network operators were required to provide the caller's location and phone number to be called back together with public emergency services. Later, similar requirements were introduced in Europe and Japan, which eventually brought up the appearance of LBS—calling equipment-based geography location service. After that, rapid development of fields of Positioning Systems, Communication, and Global Information System (GIS) stimulated the industry's imagination on LBS. The service was initially widely adopted by telecom companies to provide customized services to mobile subscribers according to their geographic locations.
LBS is an important subject in most existing mainstream standards at present. Positioning technique is an aspect of LBS, and includes:
a) Network-Based Positioning Technique:
A Mobile Terminal (MT), while receiving a signal from a current serving Base Station (BS), searches for signals from other BSs. If the MT finds that a signal from another BS is stronger than a predetermined threshold, MT determines the difference of the arrival time of the signals from the BSs, so as to prepare for the combination of the two signals. Such a capability of the MT lays a technical foundation for positioning. The positioning operation platform can obtain the MT's information (e.g., information on pilot strength) through a Code Division Multiple Access (CDMA) network and thereby determine a position of the MT. Some other network-based techniques can offer better positioning precision, such as measurement of the MT's round trip delay and Angle Of Arrival (AOA) of a signal. These techniques, however, require the addition of measurement equipment on the BS, and thus increases the cost.
b) Assisted GPS Technique (AGPS):
The assisted GPS technique implements positioning operation primarily depending on GPS satellites. A MT receives signals from at least 4 GPS satellites, performs positioning calculation based on the signals, and reports the calculation result to the network. For a general GPS technique, the GPS receiver searches for available GPS satellites in a global space domain. Such a satellite search requires such a long time that this technique cannot meet the demand of rapid mobile positioning. In the assisted GPS technique, the network can determine the GPS satellites over a cell where the MT is located according to the location of the cell and provide the information to the MT. Based on the information received, the MT can narrow down the scope of search area to implement the search process more quickly. After the search process, the MT transmits the information for calculating the MT's location to the network by interacting with the network. The network uses this information to calculate the MT's location.
c) Hybrid Positioning Technique:
The hybrid positioning technique applied in a CDMA system primarily adopts the two kinds of MT-based positioning techniques mentioned above, Network-based positioning technique and AGPS. Generally, the GPS technique can offer high positioning precision. However, in many scenarios, a MT cannot capture enough GPS satellites. In this case, signals from BSs can be used by the MT to supplement the signals from satellites. In this way, practicability of such positioning is improved and indoor positioning can be realized at the expense of certain accuracy degradation.
d) MT-Based GPS Technique:
For some LBS services requiring quick and continuous positioning (e.g., real time dynamic vehicle navigation), it is necessary to refresh information on the MT location at the interval of several seconds. In this case, the AGPS technique cannot meet the time requirement. In order to reduce the time interval between two consecutive positioning processes, an MT-based GPS technique is introduced. Unlike AGPS, in the MT-based GPS technique the calculation of the location is entirely performed by the MT itself. Further, the MT is always in a GPS tracking state so that time for interacting with the network can be reduced. Unfortunately, Time To First Fix (TTFF) is substantially the same as that with AGPS. It is also necessary to obtain information on GPS satellites from the network side.
e) Dead Reckoning (DR):
With reference to a known relative reference point or start point, the direction and distance of a target object are calculated continuously during its movement. With the help of a map matching algorithm, the location of the moving target can be determined. This approach is suitable for continuous positioning of a moving object. DR depends on measurement precision on the MT's acceleration, velocity, and moving direction. Corresponding measurement information can be provided by means of an odometer, gyroscope, accelerometer, etc.
f) Approaching-Type Positioning:
The location of a moving object is determined by estimation based on the nearest fixed reference detection point. The cell ID-based approach can be regarded as one branch of the approaching-type positioning technique. Estimation of the MT can be obtained with the nearest BS or sector.
The existing techniques have their own advantages and disadvantages. In the case of a single cell, including the case that signals from other cells are overlaid in the cell, positioning approaches based on multi-cell signal detection cannot work. The cell ID-based positioning approach has poor precision, and the GPS-based solution has relatively higher cost.